The object of the invention is a method and an instrument for locating pipeline damage by acoustically monitoring the soil surrounding the defective pipe and detecting the emission noise by means of microphones connected to the input of an amplifier that controls a noise peak display.
Electronic pipeline damage detectors operating on the "listening principle" have been successfully used for years. Yet, there are recurrent cases where pipe breaks cannot be found in spite of the greatest instrument amplification (1.1 million). As a consequence, one must put up with unwarranted digging, because the instrument gives a clear indication that a break may be assumed at some given place or other. The reason for these phenomena lies in the physics of a pipe break. The medium water is known to flow out of the pipe under pressure and against the surrounding soil.
At the emission point of this stream of water, solid-borne sound is generated, which spreads spherically. It travels to the surface for one and, for another, induces the pipeline to oscillate via the soil. Depending on the impact pressure, the resonance characteristics of the pipe, and the solid-borne sound attenuation of the soil, different frequencies and intensities may occur at the surface. Apart from that, reflection occurs in the vicinity of foundation walls, gully holes, etc., which are superimposed on the actual leakage noise.
The sound conductivity of steel, cast iron, and plastic pipes varies significantly. The sound conductivity of plastic pipes, be they PVC, PE, or AC, is very low. In measurements, it may be neglected. Because of this situation, the interval between measurement points must be handled differently in the microphone listening method. In accordance with FIG. 1, a measurement point interval of about 3 m is sufficient for steel pipe. For cast iron pipes 1.50 m are required, and for plastic pipe 0.75 m. When the intervals chosen to acoustically monitor a pipeline are too large, there is a risk that a leak will be missed. This problem is to be expected, especially in the case of a nonmetallic pipe with a punctual propagation zone of the solid-borne sound.
If a noise is detected above the line, this need not necessarily be the expected leakage noise. Solid-borne sound waves are common in the soil and can easily simulate a leak. Momentary events, such as knocking, hammering, rattling, etc. are recognized as interference by the ear as well as the instrument and do not cause any special problem. But the situation is different with continuous vibrations that take the form of continuous noise. These interference vibrations may originate in transformers, motors, compressors, bearings, etc. Technical equipment and machinery firmly anchored in the foundations of buildings generate a large number of solid-borne oscillations, which are generally very well conducted by the soil. These vibrations, however, generally have entirely different frequencies than those originating from the leak. If the measuring technician is capable of distinguishing frequencies by ear, he is capable of detecting the actual leakage frequency in a whole spectrum of frequencies. The volume indicator of his amplifier is of little help, since it only indicates the loudest frequency, even if this is the interference frequency. In order to deal with the cited difficulties, a completely new pipeline rupture detector has been developed. Its essential innovations are:
1. memory for measurement values PA1 2. frequency analysis PA1 3. octave filter PA1 70--106--160--240--360--540--800--1,800 cps.
Pipeline rupture detection is conducted in the form of a series measurement, i.e. the ground microphone is set up at suitable intervals above the pipeline, and the location with the largest solid-borne sound intensity is determined. For this purpose the ground microphone must be repeatedly moved in the area of the leak, in order to find the culmination point, i.e. the location of the highest solid-borne sound intensity. The measurement technician must concentrate on each measurement, i.e. each new setup of the ground microphone, and must adapt himself physically and psychologically to the measurement. This adjustment cannot be expected of a single person indefinitely, because of fatigue, introducing another chance that a signal will be overheard or misinterpreted.
The present invention has made it its task to significantly improve a method for locating pipeline ruptures of the initially cited kind and an instrument operating on that principle. Specifically, location was to be made faster, more accurate, and operationally safer.
In the solution of this problem, the method is characterized in that, in a first process phase, the noise peak of each measurement point, detected by the amplifier, is transmitted to a digital memory for measurement values, which displays a histogram of the noise distribution along the measurement distance above the pipe, and that, in a second process phase, the main and preferred frequency of the loudest measurement point is determined on a broad band and that an octave filter is used to determine the characteristic frequency of the emitted medium from the main and preferred frequency as determined at a broad band, for the purpose of precise location.
The new method utilizing an electronic memory for measurement values eliminates these shortcomings. The instrument has eight such memories, which are successively activated. At measurement point 1, the noise recorded by the ground microphone is also displayed on a linear scale of light emitting diodes.
The scale covers a range from 0 to 10. Only the highese point of a measurement value appears. This LED scale is brightness controlled, so that it can be conveniently read, even in bright daylight. At night the usual illumination of the scale is obviated.
When a measurement value is to be stored, the scale value is transmitted to an electronic memory and can be held there for hours. Then measurement point "2" is monitored, and the solid-borne sound occurring at that point is displayed on the second scale. This value is subsequently also stored. Eight measurement points are thus successively checked, and their measurement values recorded. After activation and display of all eight measurement values, these can all be observed at the same time, and one can easily recognize the measurement point at which the greatest solidborne sound intensity was measured. The line connecting the top scale markings thus provides a volume diagram for the tested distances.
The memory for measurement values is also used to locate the general area of leaks in the water pipe network. To date, the values obtained with a probe at accessible contact points had to be recorded in order to find the loss section between two listening points. Here, one measurement value after another is stored, and in the "poll" mode one then obtains accurate information between which measurement points the loss line lies.
As pointed out above, the place of the greatest volume need not be the leak. For this reason, the noise, resp. frequency spectrum occurring at this point is analyzed, i.e. the individual frequency components are determined. This differentiation of different frequencies, which is not always easy for the human ear, is performed electronically by this instrument. The eight LED scales are each allocated to a certain frequency. The frequency from one step to the next is always 1.5 octaves and covers the frequency range from 70 cps to 1,800 cps which is relevant to leak detection.
These frequencies are specifically:
For frequency analysis, the geophone is set up at the loudest measurement point, and broad band amplification is selected to keep signals from exceeding the scale range. The individual scales then indicate the intensity of their associated frequencies. One can thus determine, for example, the main and preferred frequency of leakage noises without involving the human ear. Empirically, frequencies above 600 cps are unusual in leak location and must therefore be regarded as interference frequencies.
Precision location is the next step. In order to allow it to filter out interference frequencies, the instrument is switched from its previous broad band mode to a filter amplifier mode. Eight highly selective electronic filters, in octave spacing, are available for this purpose. The leak frequency, determined by means of frequency analysis, is selected in one of the eight filters, so that the amplifier now singles out this frequency for amplification, suppressing other, interference, frequencies to a large extent. This guarantees that for precision location only the actually interesting frequency is amplified, monitored, and measured. This prevents a wrong filter setting, which is unavoidable without frequency analysis.
The interaction of these three new assemblies, in conjunction with an industry-proven, low noise amplifier, allows faster and more accurate pipe leak location. The burden on the measurement personnel is also reduced, so that greater efficiency may be expected in this respect as well.
The object of the present invention arises not only out of the object of the individual patent claims, but also out of the mutual combination of the individual patent claims.
All of the statements and characteristics revealed in the documentation, especially the spatial configuration represented in the drawings, are claimed as being essential to the invention, insofar as they are new with respect to the state of the art, either singly or in combination.
The invention is explained in greater detail below, using drawings that illustrate only one possible implementation. The drawings and their description reveal other features and advantages of the invention, which are essential to the invention.